A known intake system includes an intake control valve (hereinafter referred to as a tumble control valve) and an actuator to control supply of intake air to an internal combustion engine, which has a plurality of cylinders. The tumble control valve generates an intake air vortex (a tumble flow), which flows in a combustion chamber of each cylinder around an axis perpendicular to an axis of the cylinder, so that a combustion efficiency in the combustion chamber is improved to improve fuel consumption and emissions (e.g., improving HC reducing effect) of the engine. The actuator drives tumble valves, which are valve elements of the tumble control valve.
As shown in FIG. 13, the tumble control valve includes an intake manifold 1, a plurality of tumble valves 3, a valve shaft 4 and a bearing device (an oil seal 9, a bearing 10). The intake manifold 1 forms a flow passage that is communicated with the combustion chamber of each cylinder of the engine. Each tumble valve 3 opens and closes a corresponding flow passage. The valve shaft 4 is connected to the tumble valves 3 to rotate integrally with the tumble valves 3. The bearing device (the oil seal 9, the bearing 10) supports the valve shaft 4 in a slidable manner in a rotational direction of the valve shaft 4.
The intake manifold 1 includes a surge tank and a plurality of intake branch conduits. The surge tank includes a plurality of intake air outlets. The intake branch conduits are connected to the intake air outlets, respectively, of the surge tank.
In each of the intake branch conduit, a partition 13, such as a partition wall, which partitions an inside space (an intake branch flow passage) of the intake branch conduit into a first intake branch flow passage 11 and a second intake branch flow passage 12.
The first intake branch flow passage 11 and the second intake branch flow passage 12 form flow passages that are communicated with the combustion chamber of the corresponding cylinder of the engine.
The actuator includes an electric motor (hereinafter simply referred to as a motor) M, a speed reducing mechanism, and a drive force transmission apparatus. The motor M generates a rotational drive force that drives the tumble valves 3. The speed reducing mechanism reduces a speed of rotation transmitted from a motor shaft 5, which is an output shaft of the motor M. The drive force transmission apparatus transmits the rotational drive force of the motor M to the valve shaft 4 of the tumble control valve.
The speed reducing mechanism includes a worm gear 14, a helical gear 15, a pinion gear 16 and the output gear 6. The worm gear 14 is connected to the motor shaft 5 to rotate integrally with the motor shaft 5. The helical gear 15 is engaged with, i.e., is meshed with the worm gear 14 and is rotated by the worm gear 14. The pinion gear 16 and the helical gear 15 are placed along a common axis. The output gear 17 is meshed with the pinion gear 16 and is rotated by the pinion gear 16. Furthermore, the helical gear 15 and the pinion gear 16 are rotatably supported by an outer peripheral surface of a gear shaft 20, which extends in a direction perpendicular to a direction of the rotational axis of the motor shaft 5.
The drive force transmission apparatus includes the output gear (serving as a first rotatable member) 17, a gear shaft coupling (serving as a second rotatable member) 18, and a rubber cushion (a shock absorbing member) 19 (see, for example, JP2013-050207A corresponding to US2013/0035192A1). The output gear 17 and the gear shaft coupling (hereinafter simply referred to as a coupling) 18 are placed along a common rotational axis and are rotatable relative to each other. The rubber cushion 19 is made of a rubbery elastic material and can be resiliently deformed in a twisting direction about the rotational axis of the drive force transmission apparatus.
The output gear 17 includes a plurality of primary projections (hereinafter referred to as primary partitions), and the coupling 18 includes a plurality of secondary projections (hereinafter referred to as secondary partitions). The primary projections and the secondary projections are alternately arranged one after another in a circumferential direction about the rotational axis.
The rubber cushion 19 includes primary elastic bodies and secondary elastic bodies. Each primary elastic body is placed between the corresponding primary partition and the corresponding secondary partition, which are placed adjacent to each other in the circumferential direction. Each secondary elastic body is placed between the corresponding primary partition and the corresponding secondary partition, which are placed adjacent to each other in the circumferential direction. The corresponding primary elastic body and the adjacent secondary elastic body, which are placed adjacent to each other in the circumferential direction, are connected to each other through a primary bridge. The corresponding secondary elastic body and the adjacent primary elastic body, which are placed adjacent to each other in the circumferential direction, are connected to each other through a secondary bridge.
JP2013-050207A (corresponding to US2013/0035192A1) discloses two types of drive force transmission apparatuses (referred to as first and second prior art techniques).
The output gear 17 of the drive force transmission apparatus of the first prior art technique includes a gear tooth forming portion 53, a first shaft portion (not shown), and a tilted groove (not shown). The gear tooth forming portion 53 is configured into a cylindrical tubular form and is engageable with the pinion gear 16. The first shaft portion is configured into a cylindrical tubular form and is placed on a radially inner side of the gear tooth forming portion 53 to extend in the axial direction of the output gear 17. The tilted groove is configured into a spiral form (a skew form) and is formed in an inner peripheral surface of the first shaft portion (more specifically, a hole wall surface of a through-hole that extends through the first shaft portion).
Furthermore, the coupling 18 of the first prior art technique includes a second shaft portion and an engaging pin. The second shaft portion is fitted into the through-hole of the first shaft portion of the output gear 17. The engaging pin projects from an outer peripheral surface of a distal end part of the second shaft portion.
The through-hole extends through the inside of the first shaft portion such that the second shaft portion of the coupling 18 is insertable into the through-hole from one end side (inserting side) of the first shaft portion toward the other end side of the first shaft portion. The through-hole extends along a central axis of the first shaft portion.
Now, an assembling procedure of the drive force transmission apparatus of the first prior art technique will be briefly described.
First of all, in a state where the rubber cushion 19 is installed to the output gear 17, at the time of installing the second shaft portion of the coupling 18 into the through-hole of the output gear 17, the engaging pin of the coupling 18 is moved from a start end to a terminal end of the tilted groove, so that the engaging pin of the coupling 18 is moved through the tilted groove.
At this time, the primary elastic bodies and the secondary elastic bodies of the rubber cushion 19 rotate the output gear 17 relative to the coupling 18, so that the rubber cushion 19 is elastically deformed in a twisting direction about the rotational axis of the drive force transmission apparatus.
Then, when the engaging pin is moved beyond the tilted groove, each of the primary and secondary elastic bodies is elastically restored to its original form, so that the output gear 17 is rotated relative to the coupling 18 in an opposite direction, which is opposite from the twisting direction of the primary and secondary elastic bodies of the rubber cushion 19. Thereby, the engaging pin is returned to a position, at which an engaging portion, which is formed in an opening edge part of the through-hole at the opposite side of the through-hole that is opposite from the inserting side, is engageable with the engaging pin.
In this way, the engaging pin can limit movement of the output gear 17 and the rubber cushion 19 relative to the coupling 18. Thereby, it is possible to limit unintentional disassembling or an unintentional positional deviation of the components of the drive force transmission apparatus at the time of transportation, the time of component assembling, or the time of operation of the drive force transmission apparatus.
Next, the drive force transmission apparatus of the second prior art technique will be described. The second shaft portion, which is fitted into the through-hole of the output gear 17, is formed in the coupling 18 of the drive force transmission apparatus of the second prior art technique. A plurality of resilient engaging pieces (snap fit parts) is formed in the distal end side of the second shaft portion. The resilient engaging pieces are resiliently radially inwardly deformed at the time of moving in the through-hole. Thereafter, when the resilient engaging pieces are moved beyond the through-hole, the resilient engaging pieces are resiliently restored. Thereby, the resilient engaging pieces are engaged with the engaging portion, which is formed in the opening edge part of the through-hole at the opposite side that is opposite from the inserting side.
At this time, the output gear 17 is urged by the elastic restoring force of the respective primary and secondary elastic bodies of the rubber cushion 19 toward the opposite side, which is opposite from the inserting side of the through-hole, so that an engaging part of each resilient engaging piece always contacts the engaging portion, which is formed in the opening edge part of the through-hole. Thereby, it is possible to limit movement of the output gear 17 and the rubber cushion 19 relative to the coupling 18 in the direction of the rotational axis of the drive force transmission apparatus, so that unintentional disassembling of the drive force transmission apparatus can be limited.
In the drive force transmission apparatus of the first prior art technique, when the actuator is stopped and is left under a cold environment in a twisted state where the rubber cushion 19 is twisted after the operation of the actuator, the rubber cushion 19 is hardened while maintaining the twisted state. At this time, when the engaging pin of the coupling 18 is moved to the terminal end of the through-hole of the output gear 17, which is used at the time of fitting the output gear 17 and the coupling 18 together, the engaging pin may be disengaged from the engaging portion formed in the opening edge part of the through-hole and may enter the inside of the through-hole upon application of vibrations generated at the time of starting the engine. When the engaging pin enters the inside of the through-hole, an engaging state between the pinion gear 16 and the output gear 17 is changed. This will result in generation of an excess stress to the output gear 17 to disadvantageously cause breakage of output gear teeth of the output gear 17 or a reduction in the lifetime of the output gear 17.
Furthermore, in the drive force transmission apparatus of the second prior art technique, in order to limit the disengagement of the resilient engaging pieces caused by the low temperature and the vibrations, the snap fit structure is used. However, due to the snap fit structure, the rigidity of the rotatable shaft portion is reduced. Thereby, when the torque is applied to the output gear 17, the resilient engaging pieces cannot withstand the applied force and are tilted. As a result, the tooth contact surfaces between the pinion gear 16 and the output gear will be changed.
For example, an excessive stress may be generated due to a decrease in the contact surface area of each of the output gear teeth. Also, an excessive stress may be generated due to a change from a line-to-line contact of a pinion gear tooth surface of the pinion gear relative to an output gear tooth surface of the output gear to a point-to-point contact of the pinion gear tooth surface of the pinion gear relative to the output gear tooth surface of the output gear. When the excessive stress is generated, it will disadvantageously cause breakage of the output gear teeth of the output gear 17 or a reduction in the lifetime of the output gear 17.